Support orthopaedic device for a knee joint

ABSTRACT

Support orthopaedic device ( 1 ) for a knee joint, comprising a proximal connector ( 2 ) and a distal connector ( 3 ), articulated among themselves and respectively intended to be associated with a proximal bone ( 100 ) and a distal bone ( 101 ) of a lower limb connected among themselves by a knee joint. The device comprises a first rod ( 4   a ) and a second rod ( 4   b ), which are hinged, according to hinging axes normal to a median excursion plane of the orthopaedic device ( 1 ), to the proximal connector ( 2 ) and to the distal connector ( 3 ) so as to form with them an articulated quadrilateral. The articulated quadrilateral is planarly mobile according to a plane parallel to the excursion plane between a configuration corresponding to an extended position of the knee joint and configurations corresponding to bendings of different entity of the knee joint; the relative motion imposed to the proximal and distal connectors ( 2, 3 ) by the articulated quadrilateral is consistent with the physiological movement of the knee joint.

FIELD OF APPLICATION

The present invention relates to a support orthopaedic device for a kneejoint.

In particular, the device is of the type comprising a proximal connectorand a distal connector, articulated to each other and respectivelyintended to be associated to a femoral bone and to a tibial bone of thelower limb of a patient, these bones being connected to each other bymeans of a knee joint.

PRIOR ART

The knee joint compartment may be subject to surgical operations fortrauma or corrective treatment. Such operations, as in the general caseof any orthopaedic operation, are characterized by a post-operationalperiod, in which the ossification process takes place; in this phase, itis generally necessary to ensure that the joint is not subject toexcessive loads.

The unloading of the joint may be obtained by total immobilization ofthe knee; on the other hand, this solution has substantial therapeuticdrawbacks, and is therefore often not used.

A known alternative solution foresees the use of an orthopaedic device,of above said type, which is provided for allowing partial or totaltransmission of loads through the operated joint.

In these cases, the proximal and distal connectors are generallyassociated to anchoring devices, which are respectively associated tofemoral and tibial bone of patient.

A primary drawback of known orthopaedic devices is the articulationbetween the two connectors. In fact the relative movement imparted tothe two connectors has to be unitary and above all has to reproduce inthe most faithful manner possible the movements of the anchoring bones,which are physiologically determined by the natural joint. Suchfunctional condition has not been ensured by means of a simple andefficient constructive morphology. In fact, the coupling provided by theknee joint foresees a combination of rotations and relative slippingamong the two affected bones, whose kinematics are difficult toreproduce with a reliable and small sized mechanism. In fact, such acoupling cannot be assimilated to a simple hinge having a fixedrotational axis. In each case, a system is provided which allows thedistraction of the joint, by moving the articulation contact surfacesfarther away from each other, in order to allow a minimal rotationalmovement, even if the device does not faithfully reproduce the joint.

A second problem arising from the therapeutic use of orthopaedic devicesaccording to the known art is the precise positioning of the same devicewith respect to the bone structure of the patient. In particular, it isof fundamental importance that the articulation of the two connectors isprovided along a plane which is normal to the articulation axis of thelower limb. The known anchoring devices are associated, by means ofscrews, to suitable bone sites of femur and tibia. The bone surface insuch sites is not normal with respect to the articulation axis;therefore a morphological reference for guiding the fixing operations ofthe orthopaedic device is absent. Moreover, the attachment sites arerelatively remote from the joint compartment, further complicating theproblem regarding a proper positioning of the orthopaedic device.

The technical problem which the present invention has to solve istherefore to provide an orthopaedic device having a structure such as toovercome above said drawbacks of the known art.

SUMMARY OF THE INVENTION

Above said technical problem is solved by an orthopaedic device of abovesaid type, also comprising a first rod and second rod, which are hingedto each other, according to hinging axes normal to a median excursionplane of the orthopaedic device 1 itself, to the proximal connector andto the distal connector so as to form with them an articulatedquadrilateral. The articulated quadrilateral is planarly mobileaccording to a plane parallel to the excursion plane between a mainconfiguration corresponding to an extended position of the knee jointand a plurality of secondary configurations corresponding to bendings ofdifferent entity of the knee joint; in particular, the relative motionimposed on the proximal and distal connectors by the articulatedquadrilateral is consistent with the physiological movement of the kneejoint.

In general, the idea of the present invention is to reproduce theflexing and extending movements of the knee joint by means of anarticulated quadrilateral, two opposed members of which are provided bythe connectors.

This constructive solution allows for a reduced size and complexity ofthe orthopaedic device, on the other hand ensuring a relative movementamong the different elements, which reproduces, in a sufficientlyfaithful manner, the physiological movement of the joint.

An advantage of the invention is the fact that the device according tothe present invention is easily positioned and modularly assembled withother known orthopaedic devices, ensuring a fast and precise implant.

Further characteristics and advantages will be more clearly understoodfrom the following detailed description, of a preferred embodiment,which is not limiting, of the present invention, with reference toattached figures, which are only illustrative but not limiting in scope.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an isometric view of an orthopaedic device according to theinvention,

FIG. 2 shows an exploded view of various components of orthopaedicdevice of FIG. 1,

FIG. 3 shows an isometric view of orthopaedic device of FIG. 1,associated to a knee joint, which is extended by means of knownanchoring devices,

FIG. 4 shows an isometric view of elements represented in FIG. 3, from adifferent perspective,

FIG. 5 shows an isometric view of elements represented in FIG. 3, with aflexed knee joint,

FIG. 6 shows a front view of a tibia-femur group, to which theorthopaedic device of FIG. 1 is associated by means of known anchoringdevices,

FIG. 7 shows a diagram reproducing the kinematics of the articulatedquadrilateral facilitating articulation of device of FIG. 1.

DETAILED DESCRIPTION

With reference to the appended figures, reference numeral 1 indicates asupport orthopaedic device for a knee joint. The primary task of such adevice, as already said, is to transmit the same the loads which wouldotherwise act on the joint, allowing, during the post-surgery period, aproper healing and at the same time ensuring an at least partialmobility of the affected lower limb.

The orthopaedic device 1 comprises a proximal connector 2 and a distalconnector 3, which are articulated to each other and are respectivelyprovided to be associated to a proximal bone 100 and distal bone 101 ofa lower limb, which are connected to each other by means of the kneejoint. In particular, in the preferred embodiment of the appendedfigures, the proximal bone 100 is the femur of the patient, whereas thedistal bone 101 is advantageously the tibia.

Said orthopaedic device 1 also comprises a first rod 4 a and a secondrod 4 b, said rods 4 a, 4 b being hinged, according to hinging axeswhich are normal to a median excursion plane of same device, to proximalconnector 2 and distal connector 3, in order to form an articulatedquadrilateral with them.

The articulated quadrilateral, which is schematically shown in FIG. 7,is therefore comprised of a frame operatively provided by proximalconnector 2, two balance beams which are provided by rods 4 a and 4 band by a push rod, which is provided by distal connector 3.

The articulated quadrilateral is planarly mobile according to a planewhich is normal to the excursion plane between a main configurationcorresponding to an extended position of the knee joint and a pluralityof secondary configurations corresponding to bendings of differententity of the knee joint; the relative motion imparted to the proximaland distal connector 2, by the articulated quadrilateral is consistentwith the physiological movement of the knee joint.

As can be seen in attached FIGS. 3-6, the proximal connector 2 oforthopaedic device 1 is provided for direct connection to a firstanchoring device 5, which is provided for being fixedly associated toproximal bone 100, i.e. the femur; whereas the distal connector 3 isprovided for direct connection to a second anchoring device 6, providedfor being fixedly associated to distal bone 101, i.e. the tibia.

The first anchoring device 5, in the preferred embodiment, comprises alongitudinal rail 50, provided with at least a first clamp 51 which maybe associated to a femoral surface by means of an assembly of bonescrews. The bone screws are advantageously inserted on a suitablefemoral surface, which, as previously said, has a longitudinal axis xwhich is not perpendicular to joint axis y of limb (in particular, theangle between the two is approximately 81°). The first clamps 51 may beoriented with respect to longitudinal rail 50. The attachment site ofthe bone screws is preferably located on a lateral surface of the femur;therefore device 1, which is rigidly fixed to distal end of longitudinalrail 50, is in a lateral position with respect to lower limb.

In an alternative embodiment, not shown, of present invention, the firstanchoring device 5 may comprise a ring, or a ring portion, which isconnected to proximal connector 2.

As can be readily seen in FIG. 6, a compressor 70 may be associated tofirst anchoring device 5, in order to distract both distal 3 andproximal connectors 2, in order to form a space in the joint. Once thejoint has been distracted, indicatively by 2-10 mm, the compressor maybe removed.

The second anchoring device 6 comprises a rigid half ring 60 and asecond clamp 61, which may be associated to tibial surface by means ofbone screws, which is fixed to the latter. Due to the provision of therigid half ring, it is possible to associate the bone screws of secondclamp 61 to front surface or middle-front surface of the tibia, takingadvantage of the most suitable sites for such an implant.

As discussed before, for a proper operation of the orthopaedic device,the excursion plane of the device has to be normal to the articulationaxis of the lower limb, identified by x in FIG. 6. In order to ensuresuch condition of orthopaedic device 1, it comprises means for precisepositioning of at least one of the proximal or distal connector 2, 3with respect to the corresponding bone, i.e. the femur for proximalconnector 2 or the tibia for distal connector 3.

In particular, said means for precise positioning comprise a firstportion 20 a of one of the connectors 2, 3, which has at least areference hole 20 to temporarily receive a guide thread 200 which isfixed to the bone in correspondence to the connector; advantageously,the reference hole 20 is normal to the excursion plane.

In the preferred embodiment shown, the first portion 20 a is provided onthe proximal connector 2, and the reference hole 20 is positioned on adistal end of connector 2, with respect to the proximal bone 100 towhich it is associated. In this way, as shown in FIG. 4, the guidethread 200 is suitably introduced in a cannula screw which is insertedin the medial epicondyle 102 of the patient. By means of morphologicalreferences near the epicondyle, the cannula screw can be readilypositioned so that it is parallel to articulation axis y of the knee.The guide thread 200 is also parallel to articulation axis y and itsinsertion in the reference hole 20 causes the excursion plane oforthopaedic device 1 to be orthogonal to this axis. The guide thread 200has no structural purpose and is removed once the orthopaedic device 1has been implanted.

From an operational point of view, a method for fixing the deviceaccording to the invention to the bone structure of a patient comprisesthe following steps: an insertion step of a thread in the femoralchannels according to a direction parallel to articulation axis y of thelimb, followed by anchoring of the proximal connector 2 and the distalconnector 3 to the bone structure of patient, by means of said anchoringmeans 5, 6.

In the diagram of FIG. 7, the positions of the members forming thearticulated quadrilateral in the case of the main configuration and of asecondary configuration corresponding to bending at a substantiallyright angle of the knee joint are shown. In the diagram the trajectoryof a point of the distal connector 3 corresponding to a change ofbending angle of tibia, with a fixed position of the proximal connector,is also shown. Such a trajectory, which is substantially the same as thetrajectory provided by the articular movement of a healthy knee, isobtained by the following constructive means.

First of all, the articulated quadrilateral used is a Grashof mechanism,in which the relative excursion of links is however operatively limitedat least by the anchoring to the bone structures of the lower limb.

The first and second rod 4 a, 4 b which comprise the quadrilateral,cross each other at least in its main configuration. In particular, thequadrilateral remains inverted for the better part of its operativeconfigurations, wherein by operative configurations one refers to themain configuration and secondary configurations which are operativelyfeasible. The inverted position of the quadrilateral allows the instantcentre of rotation of the device to be held inside the quadrilateral'svolume, thereby constraining the instant axis of rotation near the kneejoint. In fact, as per Chasles' theorem, the instant centre of rotationis at the crossing C of the longitudinal axes z′, z″, shown in FIG. 7,of the two rods 4 a, 4 b, which form the balance rods of thequadrilateral.

In particular it is advantageous if an inversion configuration, i.e. adead point configuration, belongs to the group of secondaryconfigurations; in this case such a configuration corresponds to abending at a substantially right angle of the knee joint.

Advantageous dimensional characteristics of the articulatedquadrilateral according to the invention comprise: a ratio between thedistance between hinging axes with first and second rods 4 a, 4 b ofdistal connector 3 and the distance between hinging axes with first andsecond rods 4 a, 4 b of the proximal connector 2 higher than 1, andpreferably comprised between 3.5 and 4.3 (the value of the ratio in theillustrated embodiment is 43/11); a ratio of the distances of theopposed hinging axes in relation to first and second rods 4 a, 4 bbetween 0.9 and 1.1 and preferably equal to 1, as in the illustratedembodiment; ratio of distances of the opposed hinging axes of first rod4 a and the distance between the hinging axes of first and second rods 4a, 4 b of distal connector 3 higher than 1 and preferably lower than 1.2(the value of the ratio in the illustrated embodiment is 47/43).Obviously, all these values are absolutely non-limiting with referenceto the present invention.

The orthopaedic device 1 according to the invention advantageouslycomprises: first locking means 30 provided for allowing locking of thearticulated quadrilateral in the main configuration or in any one of itssecondary configurations; second locking means 34 provided for allowingthe locking of the articulated quadrilateral in a finite plurality ofpossible locking configurations; stop means 37 adjustable forunilaterally limiting the excursion of the articulated quadrilateral inorder to inhibit bending of the knee joint to which the device 1 isassociated, which are greater than a desired angle.

At least one of first and second rod 4 a, 4 b comprises a firsttransversal threaded hole 40 a, with axis normal to the excursion planeof device 1; the first locking means 30 comprise a locking screw 31,insertable into the first transversal hole 40 a and into a slot 32 of afirst septum 33, integral with one of the distal or proximal connectors2, 3. Therefore the locking screw 31 may be clamped against the wall ofthe first septum 33 peripheral to slot 32, allowing the articulatedquadrilateral to be locked in a desired configuration.

At least one of the first and second rods 4 a, 4 b features a secondtransversal hole 40 b with axis normal to the excursion plane of thedevice 1. The second locking means 34 comprise a second septum 36integral with one of the distal or proximal connectors 2, 3, whichfeatures a plurality of locking holes 35 a, 35 b (although, as said, thereal locking of the device is preferably obtained by means of lockingscrew 31 of first locking means 30, and these holes are mainly used asreferences for the degree of articulation bending). Each of the lockingholes 35 a, 35 b is aligned with the second transversal hole 40 b at apossible locking configuration. In these configurations, it suffices toinsert a pin through the two holes to lock the rod to the connector,therefore locking the articulated quadrilateral in the desired lockingconfiguration.

In the preferred embodiment shown, the two locking holes 35 a, 35 ballow the articulated quadrilateral to be locked in above said mainconfiguration, and in a secondary configuration corresponding to a rightangle bending of the limb associated to device 1.

The stop means 37 comprise a stop screw 38, insertable into a threadedstop hole 39. The stop hole 39 is integral with one of the connectors 2,3 and has an axis which is parallel to the excursion plane of device 1.The end of the stop screw 38 opposite the clamping one is provided inorder to interfere by contact with the movement of at least one of therods 4 a, 4 b, limiting the excursion of the articulated quadrilateral.In this case, it is provided for interfering with rotation of the secondrod 4 b.

A rotation of the locking screw 38 about its axis corresponds to itstraversing along the axis of locking hole 39; in this way it is possibleto modify the position of the end of the screw provided for limiting theangular excursion of rod 4 a, 4 b, by adjusting the maximum bendingangle of the device. Advantageously, the screw and the articulatedquadrilateral are formed in order to provide a substantially linearrelationship between the angle of rotation of the screw and variation ofthe maximum excursion angle of the limb associated to the device 1.

Structurally, the first septum 33, the second septum 36 and stop hole 39are all integral with the distal connector 3. In particular, such distalconnector comprises a base 3 a, from which two lateral walls laterallyrise, forming a hinging bracket for first rod 4 a and second rod 4 b.These lateral walls are parallel to the excursion plane of device 1 andare contiguous to both hinged rods 4 a, 4 b. The first septum 33 andsecond septum 36, as shown in the appended figures, are part of one ofsuch walls.

The first transversal hole 40 a is provided on the first rod 4 a,whereas the second transversal hole 40 b is provided on the second rod 4b. The rods are preferably identical, with a first segment hinged todistal connector 3, having a transversal extension equal to the distancebetween the lateral walls of the connector; a second segment, hinged toproximal connector 2, having a reduced transversal extension in order toallow the two members to cross without interference.

Slot 32 has a circular arc shape with centre on the hinging axis offirst rod 4 a to distal connector 3. The terminal portion of lockingscrew 31, when unclamped, slides within this circular arc; in any case,slot 32 limits the angular excursion of first rod 4 a.

The two lateral walls of distal connector 3, which are inferiorly joinedby base 3 a, are joined on the upper side by cross beams 3 b. Such crossbeams are lateral with respect to the free central space inside of whichthe first and second rod 4 a, 4 b may move.

One of the beams 3 b, in particular the one nearer to second rod 4 b,has a stop hole 39 for inserting the stop screw 38. This beam also has ahole with axis normal to that of the stop hole 39, inside which a screwis inserted, for interfering with the stop screw 38 in order to lock itin the desired position.

The base 3 a of the distal connector 3 is provided for association withabove said rigid half ring 60, which is mounted in a distal positionunderneath the same. To this end, the base 3 a provides suitableconnecting means, i.e. a central hole 300 on the bottom of the bracketdefined by the lateral walls, as well as longitudinal slots 301 providedon a portion of the base which is not surmounted by lateral walls. Theseopenings allow insertion of fixing screws of the rigid half ring 60, asshown in FIGS. 3-6.

The proximal connector 2 comprises, at its distal end (always referringto the femoral bone, to which it is associated) two side-by-sidebrackets, into which the second segments of first rod 4 a and second rod4 b are inserted and hinged, according to parallel but offset axes.Reference hole 20, which is preferably a through hole, is provided onthe distal end of both brackets, in a lateral position with respect tothe central free space inside of which first and second rod 4 a, 4 b maymove.

The proximal portion of the proximal connector 2 is advantageouslyarranged in such a way as to be associated to a longitudinal rail 50 ofabove said type. To this end, it comprises suitable connection means,i.e. two shaped and parallel grooves 21 and at least one main threadedseat 22 for inserting a locking member 23 of the longitudinal rail.

Obviously, in order to meet contingent and specific needs a personskilled in the art may introduce various modifications and variations toabove said orthopaedic device, which are all within the scope ofprotection of the invention, as defined by the following claims.

1. Support orthopaedic device (1) for a knee joint, comprising aproximal connector (2) and a distal connector (3), articulated amongthemselves and respectively intended to be directly connected to a firstand to a second anchoring device (5, 6), arranged to be integrallyassociated respectively with a proximal bone (100) and a distal bone(101) of a lower limb connected among themselves by a knee joint;characterised in that it comprises a first rod (4 a) and a second rod (4b); said first and second rods (4 a, 4 b) being hinged, according tohinging axes normal to a median excursion plane of the orthopaedicdevice (1), to the proximal connector (2) and to the distal connector(3) so as to form with them an articulated quadrilateral; saidarticulated quadrilateral being planarly mobile according to a planeparallel to the excursion plane between a main configurationcorresponding to an extended position of the knee joint and a pluralityof secondary configurations corresponding to bendings of differententity of the knee joint, the relative motion imposed to the proximaland distal connectors (2, 3) by the articulated quadrilateral beingconsistent with the physiological movement of the knee joint, saidproximal connector (2) presenting, in correspondence with one of itsdistal ends, a reference hole (20), normal to the excursion plane,intended to temporarily house a guide thread (200) integral with theproximal bone (100) to allow the accurate positioning of the connectorwith respect to the bone.
 2. Orthopaedic device (1) according to claim 1wherein said proximal connector (2) presents connection means (21, 22,23) arranged to hold a longitudinal rail (50) of the first anchoringdevice (5).
 3. Orthopaedic device (1) according to claim 1 wherein saiddistal connector (3) presents connection means (300, 301) arranged tofasten the connector to a rigid half ring (60) of the second anchoringdevice (6).
 4. Orthopaedic device (1) according to claim 1 wherein thefirst rod (4 a) and the second rod (4 b) are crossed at least in themain configuration.
 5. Orthopaedic device (1) according to claim 4,wherein the ratio between the distance between the hinging axes with thefirst and the second rods (4 a, 4 b) of the distal connector (3) and thedistance between the hinging axes with the first and second rods (4 a, 4b) of the proximal connector (2) is comprised between 3.5 and 4.3. 6.Orthopaedic device (1) according to claim 5, wherein the ratio betweenthe distances of the opposite hinging axes in relation to the first andsecond rods (4 a, 4 b) is comprised between 0.9 and 1.1.
 7. Orthopaedicdevice (1) according to claim 6, wherein the ratio between the distanceof the opposite hinging axes of the first rod (4 a) and the distancebetween the hinging axes with the first and second rods (4 a, 4 b) ofthe distal connector (3) is comprised between 1 and 1.2.
 8. Orthopaedicdevice (1) according to claim 1, comprising first locking means (30)arranged to allow the locking of the articulated quadrilateral in themain configuration or in any one of its secondary configurations. 9.Orthopaedic device (1) according to claim 8, wherein at least onebetween the first and second rods (4 a, 4 b) features a firsttransversal threaded hole (40 a) with axis normal to the excursion planeof the device (1); the first locking means (30) comprising a lockingscrew (31), insertable into the first transversal hole (40 a) and into aslot (32) of a first septum (33) integral with one of the distal orproximal connectors (2, 3); said screw being clampable against the wallof the first septum (33) peripheral to the slot (32) to lock thearticulated quadrilateral in a wanted configuration.
 10. Orthopaedicdevice (1) according to claim 9, wherein the first transversal hole (40a) is arranged on the first rod (4 a), the first septum (33) beingintegral with the distal connector (3), parallel to the excursion planeof the device (1) and contiguous to the first rod (4 a), the slot (32)having the shape of an arc of circle with the centre on the hinging axisof the first rod (4 a) to the distal connector (3).
 11. Orthopaedicdevice (1) according to claim 1, comprising second locking means (34)arranged to allow the locking of the articulated quadrilateral in afinite plurality of possible locking configurations.
 12. Orthopaedicdevice (1) according to claim 11, wherein at least one of the first andsecond rods (4 a, 4 b) features a second transversal hole (40 b) withaxis normal to the excursion plane of the device (1); the second lockingmeans (34) comprising a second septum (36) integral with one of thedistal or proximal connectors (2, 3), which features a plurality oflocking holes (35 a, 35 b), each of which is aligned with the secondtransversal hole (40 b) at a possible locking configuration, a pin beingtherefore insertable through the two holes to lock the articulatedquadrilateral in the wanted locking configuration.
 13. Orthopaedicdevice (1) according to claim 1, comprising stop means (37) adjustableto unilaterally limit the excursion of the articulated quadrilateral soas to not allow bendings of the knee joint, with which the device (1) isassociated, greater than a wanted angle.
 14. Orthopaedic device (1)according to claim 13, wherein the stop means comprise a stop screw(38), insertable into a threaded stop hole (39) integral with one of theconnectors (2, 3) and with axis parallel to the excursion plane of thedevice (1), the end of the stop screw (38) opposite the clamping onebeing arranged to interfere by contact with the movement of at least oneof the rods (4 a, 4 b) by limiting the excursion of the articulatedquadrilateral.
 15. Orthopaedic device (1) according to claim 14, whereinthe distal connector (3) comprises two side walls which rise laterallyin relation to the base (3 a) to form a hinging bracket for the firstrod (4 a) and the second rod (4 b), said rods (4 a, 4 b) both featuringa first segment, hinged to the distal connector (3), with transversalextension equal to the distance between the side walls and a secondsegment, hinged to the proximal connector (2), with reduced transversalextension compared to the first segment to allow crossing withoutinterference of the two members; the proximal connector comprising twoside-by-side brackets, inside which, according to parallel but offsetaxis, the second segments of the first rod (4 a) and the second rod (4b) are introduced and hinged.